Photocatalytic Activity of Titania/Polydicyclopentadiene PolyHIPE Composites

Macroporous polymer composites with photocatalytic activity are prepared by the polymerization of surface modified TiO₂ nanoparticle stabilized high internal phase emulsions. Poly(ethylene glycol‐b‐propylene glycol‐b‐ethylene glycol) triblock copolymer is used to synthesize surface modified TiO₂ anatase via a sol–gel method. Macroporous composites are obtained by the ring opening metathesis polymerization of dicyclopentadiene within the particle‐stabilized high internal phase emulsion templates. Photocatalytic activity of the resulting macroporous polymer composites is described by the kinetic data of the heterogeneous photocatalytic degradation reaction of 4‐nitrophenol.     

Development of an aluminum/amorphous nano-SiO2 composite using powder metallurgy and hot extrusion processes

Ceramic nanoparticle reinforced aluminum matrix composites usually exhibit superior mechanical properties when compared to monolithic materials, particularly in severe working conditions such as elevated temperatures. Aluminum matrix nano-composites (AMNCs) are widely used for structural applications in aerospace and automotive industries due to their low density and high strength to weight ratio. The aim of this research was to study the effect of SiO₂ nanoparticles as the reinforcing phase on the mechanical properties of aluminum matrix composites. For this purpose, powder metallurgy and subsequent hot extrusion methods were used to prepare a reference sample and several Al-SiO₂ nano-composite rods, containing 1, 2 and 3 wt% nano-silica. Some sample preparation procedures for the manufacturing process, involved mixing, compaction, sintering, preheating and hot extrusion. Mechanical properties of the developed composites were investigated by macro- and micro-hardness, density measurement, tensile, cold compression and hot compression tests. A scanning electron microscope and an optical microscope were used for microstructural analysis of the composite and monolithic samples before and after the hot extrusion process. Experimental tests on aluminum matrix composites reinforced with nano SiO₂ particles revealed that adding just 1 wt% SiO₂ nanoparticle increases both hardness and tensile strength by 41.8% and 24.8%, respectively. In addition, the mechanical properties were seen to decrease with increases in the SiO₂ weight fraction. Density also decreased as the SiO₂ weight fraction increased. It can therefore be said that based on the findings of this study, the SiO₂ nanoparticle can be used as an effective reinforcing material for developing aluminum matrix nano-composites.     

Oxidation resistance,ablation resistance and in situ ceramization mechanism of Al-coated carbon fiber/boron phenolic resin ceramizable composites modified with Ti3SiC2

Inherent defect of easy oxidation limited further application of carbon fiber/phenolic resin composites in hostile environments. Herein, a combined strategy of matrix modification and fiber coating was proposed to fabricate a novel ceramizable composite containing Al-coated carbon fibers and Ti₃SiC₂ toward thermal protection materials (TPM), which offered a promising solution to challenge facing long-term thermal protection and load-bearing subject to severe oxidation corrosion and ablation in hypersonic vehicle applications. Oxidation resistance, mechanical strength evolution, phase evolution, microstructure evolution and mechanical strength failure mechanism at elevated temperatures were studied based on thermogravimetric analysis, static ablation test, mechanical test, X-ray diffraction analysis, and scanning electron microscopy coupled with energy dispersive X-ray analysis. The resulting composites exhibited outstanding oxidation resistance, with residue yield at 1600 °C and flexural strength at 1400 °C as high as 87.7% and 31.7 MPa, respectively. It was found that dense multiphase ceramics formed by reactions between Ti₃SiC₂, O₂, pyrolytic carbon (PyC) and N₂, acted as oxygen barriers and self-healing agents during static ablation. Besides, the resulting composites exhibited satisfactory ablation resistance and the linear ablation rate was as low as 0.00853 mm/s. Furthermore, ablation mechanisms were revealed based on phase identification, microstructure characterization and thermodynamic calculation analysis. It was revealed that multiphase ceramics composed of PyC, Al coatings, Ti₃SiC₂, TiC, Al₂OC and AlB₂ contributed great to the ablation resistance during oxyacetylene ablation.     

High temperature flexural strength,microstructure, phase evolution and anti-oxidation mechanism of Al-coated carbon fiber/boron phenolic resin ceramizable composite modified with TiB2 and B4C

Carbon fiber/phenolic resin composites (CF/Ph) have attracted great interests in the field of thermal protection materials for their characteristics of high specific strength and easy manufacturing. However, CF/Ph are inherently susceptible to oxidation failure at elevated temperatures. In this study, a novel Al-coated carbon fiber/boron phenolic resin ceramizable composite modified with TiB₂ and B₄C was fabricated by an impregnating and compression molding route. Thermal stability, flexural strength, microstructure and phase evolution of the resulting ceramizable composite were studied. The residue yield at 1400 °C and flexural strength after treated at 1400 °C for 15min was 90.4% and 53.1 MPa, respectively, which was increased by 15.9% and 532.1% than that without ceramizable fillers. Surface defects generated by matrix pyrolysis were well healed, and PyC and carbon fibers were covered with dense ceramic layers while the fracture surface was covered with relatively continuous ceramic layers without visible pores. Multiphase ceramics composed of TiB₂, TiO₂, TiC and PyC were identified. Furthermore, oxidation failure and anti-oxidation mechanism was revealed based on the aforementioned characterizations and thermodynamic calculation results. Oxidation resistance got enhanced markedly for synergistic effects of oxygen consuming, carbon fixation, oxygen barrier and endothermic effect, which were derived from ceramization reactions between TiB₂, B₄C, O₂, Al and PyC.     

Enhanced UV resistance of solar cooling high density polyethylene/titanium dioxide composites for long outdoor life via synergy effect of UV absorber and antioxidant

In this study, the ultraviolet (UV) resistance of high‐density polyethylene (HDPE)/titanium dioxide (TiO₂) composites was investigated. It is widely known that UV absorber could efficiently improve the UV resistance of the composites, and prevent the composites from being damaged by UV light. However, a small percentage of UV light still exist that may cause damage to material only with the assistance of UV absorber. Therefore, antioxidant was used in combination with UV absorber to further improve the UV resistance of the materials. Herein, three kinds of main antioxidants were used in combination with one kind of auxiliary antioxidant, and simultaneously UV absorber was added into the matrix material to enhance the UV resistance of the HDPE/TiO₂ composites. It was found that antioxidant could prevent the break of the molecular chains during preparation processing and reduce the rate of the photo‐oxygen degradation during UV irradiation. As the aging time increases, the crystallinity of the composites increased, but the control HDPE increased the most. The reflectance of the composites without antioxidant showed a slight decrease after UV irradiation, whereas the reflectance of the composites containing antioxidant still maintained the same level after UV irradiation. With the enhancement of the aging resistance of HDPE/TiO₂ composites, the general characters were highlighted without sacrificing the excellent solar reflectivity and great cooling performance. Besides, with the addition of antioxidant and UV absorber, excellent mechanical properties of the composites can be also achieved after UV irradiation. J. VINYL ADDIT. TECHNOL., 25:303–309, 2019. © 2019 Society of Plastics Engineers     

Preparation of polyHIPE/clay composites by using a reactive intercalant

Porous polymer composites have been synthesized by polymerizing the continuous phase of styrene/divinylbenzene high internal phase emulsions in the presence of organophilic montmorillonite clay having a novel oil‐based intercalant which is a reactive methacryl derivative of quaternized methyl oleate. The morphological features, thermal stability and mechanical properties, namely compression modulus and crush strength of the resulting composites have been investigated as a function of degree of nanoclay loading. All the composites reinforced with the clay were found to have improved thermal and mechanical properties as well as desired porous and interconnected structural morphology, as compared with the bare polyHIPE matrix. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41333.     

Filler reaggregation and network formation time scale in extruded high‐density polyethylene/multiwalled carbon nanotube composites

A high‐density polyethylene (HDPE) masterbatch containing 20.2 wt% multiwalled carbon nanotubes (MWNTs) was melt diluted with neat HDPE using two different methods: a twin screw microcompounder and a single‐screw extruder. The electrical properties of these composites were assessed using bulk electrical conductivity measurements, their mechanical properties were evaluated using tensile tests and dynamic mechanical analysis (DMA), and percent crystallinity was determined by wide angle x‐ray diffraction (WAXD) and differential scanning calorimetry (DSC). A percolation threshold (p_c) of 4.5 wt% MWNTs was found in compression‐molded samples. Extruded samples were prepared with nanotube concentrations below and above the compression‐molded percolation threshold (2 and 7 wt% MWNTs) and passed through the extruder twice before entering a low‐shear melt annealing zone. Different melt annealing times were used and their effects on the electrical and mechanical properties of the resulting quench‐cooled composites were evaluated. Results showed that extruded composites were nonconductive, indicating that a conductive nanotube network did not form on the time scale of these experiments. Annealing time also did not affect significantly the mechanical properties of the resulting solid composites. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Food Additives Reducing Volatility of Antioxidants at Frying Temperature

At frying temperature, antioxidants are lost not only by reaction with radicals formed by oil oxidation but also by decomposition and evaporation before they are able to exert antioxidant activity. In this study, it was hypothesized that an additive that can bind or interact with an antioxidant could reduce volatility of the antioxidant at frying temperature. Three synthetic antioxidants, tert‐butylhydroquinone (TBHQ), butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT), which have relatively high volatility, were used as antioxidants in this study to examine the hypothesis. Thermogravimetric analysis (TGA) experiments showed that all 22 additives tested in this study effectively reduced volatility of the antioxidants. An NMR study showed that signals of BHT shifted by addition of an additive, evidencing the interaction between the two substances in the chloroform solution. To examine the effect of these interactions on antioxidant activity, heating tests were conducted with soybean oil (SBO) containing 200 ppm antioxidants at 180 °C. Oxidation was monitored with ¹H NMR for loss of olefinic protons and bisallylic protons in SBO and with gel permeation chromatography (GPC) for polymerized triacylglycerols (PTAG). Improved antioxidant activity of the antioxidants were observed when combined with several additives tested in this study, and HPLC analysis showed that the antioxidants were effectively reserved by the additives in SBO during the heating process. The concentrations of the antioxidants retained in SBO were relatively well correlated with the antioxidant activity.     

The effect of extrusion processing conditions on EVOH/clay nanocomposites at low organo‐clay contents

Ethylene vinyl alcohol (EVOH) copolymer is studied as a host for low concentrations, up to 1 wt%, of organically treated clay. The clay develops a high interaction level with EVOH and thus high torque levels accompany the structuring process leading to the formation of nanocomposites. Extrusion residence time, successive extrusion passes, screw rotational speed, and processing temperature were all found to affect the morphology and the thermal and mechanical properties of the resulting composites. The extrusion compounded composites were subsequently injection molded. A subtle balance of processing parameters is required to achieve improved properties. Long extrusion residence times were found important for good clay dispersion in some cases, whereas in other cases an exfoliated structure was obtained already after the first extrusion pass. Two organically treated clay types processed at the same conditions were examined, and found to result in different morphology and mechanical behavior. Compression molding of extrusion compounded materials, under several extrusion conditions, was studied to illustrate the effect of shear level on the resulting morphology. The delamination level was higher after compression molding compared to that after injection molding. EVOH thermal properties and thermal stability of the related composites were also examined using differential scanning calorimetry and thermal gravimetric analysis. Higher extrusion processing temperature (220 compared to 200°C) was found to change the crystallization process of EVOH in the presence of clay, leading to significant decrease in T_m and T_c compared to that of the neat EVOH. POLYM. COMPOS., 26:343–351, 2005. © 2005 Society of Plastics Engineers     

Properties and applications of nanoclay reinforced open‐porous polymer composites

Open‐porous nanoclay reinforced polymer composites were prepared via high internal phase emulsion templating using 1,3‐butanediol dimethacrylate and surface modified montmorillonite (SM‐MMT). Organophilic clay was obtained by using a reactive intercalant—quaternary cocoamine salt having a styryl group—for surface modification of MMT. The clay modification resulted in not only intercalated silicate layers but also nanoclay particles compatible with the continuous phase of the emulsions. It was found that increasing clay amount leads to formation of hierarchical porous structure accompanied with larger cavities and interconnected pores. In this respect, cavity size of the resulting composites was found to be altered between 6.78 and 8.82 μm. On the other hand, as compared to bare composites, addition of clay particles increased compressive modulus of the resulting materials from 26.4 to 72.5 MPa. The adsorption capacities of the porous composites for methyl violet 2B were investigated by batch experiments and discussed as a function of their SM‐MMT loading. It was determined that, the dye adsorption of the composites increased with increasing nanoclay amount in the polymer matrix. Thus, the adsorption percentage of the composite loaded with 7 wt % nanoclay was found to be as high as 88%. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45522.     

Structural effect of secondary antioxidants on mechanical properties and stabilization efficiency of polyamide 6/halloysite nanotube composites during heat ageing

Hindered phenol (Irganox 1010) was combined with two kinds of secondary antioxidants [i.e., tris(2,4‐di‐tert‐butylphenyl) phosphite (Irgafos168) and tris(nonylphenyl) phosphite (TNPP)] to form antioxidant mixtures, and their influences on mechanical properties and thermo‐oxidative degradation of polyamide 6 (PA6) and halloysite nanotube (HNT) filled composites were investigated. The results showed that the antioxidant combinations provided an improvement in the oxidative induction time, decomposition temperature (T_d), processability, and tensile properties of PA6. Irganox/TNPP (1:1) was found to exhibit the best thermal oxidative resistance. The study of heat ageing in the air oven at 130 °C showed that the stabilized composites with 5 wt % of HNT could retain 92% of strength without loss of modulus. The physical characteristics of antioxidants such as low volatility and possible interaction with filler in the composites played a crucial role in stabilizing efficiency during heat ageing. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45360.     

Effect of the type and quality of antioxidant additions on properties of materials of the system Al2O3-SiC-C

Results are presented for a study of the apparent density and ultimate strength in compression of developed materials of the system Al₂O₃-SiC-C, modified by introduction of phosphate addition and complex antioxidant (Al + Si + phosphate addition). It is established that introduction of a phosphate addition together with a complex antioxidant (Al + Si) to the composition of corundum-graphite SiC-containing refractory based on an ethyl silicate binder leads to compaction of the structure and formation of materials of prescribed phase composition with increased oxidation resistance. Translated from Novye Ogneupory, No. 5, pp. 28–31, May 2008.     

LDPE‐based blends and films stabilized with nonreleasing polymeric antioxidants for safer food packaging

Several novel random copolymers of ethylene and 1‐olefin counits bearing a highly efficient phenolic antioxidant moiety placed at different distances from the polymerizable double bond were prepared in the presence of a metallocene catalyst. These copolymers were melt‐blended with an antioxidant‐free LDPE in an internal batch mixer to obtain innovative materials containing nonreleasing polymeric antioxidants suitable for safer food packaging applications. Blends and films, obtained by compression molding, were tested for their thermal and thermo‐oxidative stability by thermogravimetric analysis both in dynamic and isothermal conditions. Films containing the macromolecular antioxidants showed a longer induction time before O₂ uptake starts and, consequently, a higher degradation temperature than neat LDPE or LDPE containing a low molecular weight commercial additive. Aging tests demonstrated that the new polymeric antioxidants also exert a valid protection against photo‐oxidation. Eventually, migration tests demonstrated the absence of any trace of products containing the antioxidant moiety when the films were kept in contact with a food simulant. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Functionally graded laminated composites fabricated from MAX-phase filled preceramic papers: Microstructure,mechanical properties and oxidation resistance

This paper describes the fabrication and characterization of novel preceramic paper-derived functionally graded materials (FGMs) based on Ti₃(Si,Al)C₂ MAX phase. The FGMs with different architecture were fabricated via spark plasma sintering of stacked preceramic papers at 1250 °C for 5 min. Microstructure, phase composition and elemental distribution were analyzed by scanning electron microscopy, X-ray diffraction and energy-dispersive X-ray spectroscopy, respectively. Oxidation tests were performed in air at 1300 °C for 5 h. FGMs containing Al- and Si-enriched MAX-phase layers were formed. The fabricated materials exhibit high flexural strength (over 600 MPa), which are dependent on microstructure and composition of individual layers as well as the architecture of composites. It was found that texturing of MAX phase grains during SPS results in anisotropic hardness of the composite. The difference in the composition of the individual layers also provides a hardness gradient in the composite. It was shown that the formation of the outer layer from the Al-enriched Ti₃Al(Si)C₂ MAX phase increases the corrosion resistance of Ti₃SiC₂-based composites. The high corrosion resistance of FGMs is due to the growth of a continuous and dense Al₂O₃ oxide layer.     

Effect of antioxidants on properties and morphology of poly(acrylonitrile–butadiene–styrene)/polycarbonate blends

Poly(acrylonitrile–butadiene–styrene), polycarbonate (PC), and two types of antioxidants have been blended by an extruder twin screw. Notched Izod impact strength, tensile property, and melting flow index (MFI) were measured for the blends including different amounts of antioxidants, and morphology of the blends was investigated by scanning electron microscopy (SEM). The antioxidant action, especially on mechanical properties and the phase structure of the blends, has been studied for the undergraded samples. It was found that the phenolic antioxidant, tetrakis (3,5-di-tert-butyl-4-hydroxyhydrocinnamoyloxy-methyl) methane, C₇₃H₁₀₈O₁₂, whose commercial name is KY-7910, and phosphite antioxidant, triphenyl phosphite (TPP), (C₆H₅O)₃P, all decrease the Izod impact strength and tensile modulus of the blends and increase the elongation at break if a small amount of the antioxidants (such as less than 0.7%) was mixed into the blends. When the content of the antioxidants is increased, surpassing 0.7%, KY-7910 has little effect on impact property of the blends, but TPP made the Izod impact strength decrease and the MFI increase to a great degree. SEM results show that the two phases of ABS/PC with a weight ratio of 30/70 is cocontinuous; this structure is destroyed by addition of the two antioxidants, and in ABS/PC/antioxidants blends, the size of the ABS phase, as dispersion, does not change not much with increasing KY-7910 content, but becomes more scattered and greater with increasing content of TPP. These results are consistent with the mechanical tests. © 1994 John Wiley & Sons, Inc.     

Morphological and optical behavior of thermoset matrix composites varying both polystyrene-block-poly(ethylene oxide) and TiO2 nanoparticle content

Novel inorganic/organic epoxy based materials were fabricated using both poly(styrene-b-ethylene oxide) (SEO) block copolymer and synthesized TiO₂ nanoparticles as modifier. The influence of the ratio between modifiers on the final morphology generated in the investigated epoxy systems was studied by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Results indicated that even for high nanoparticle content, TiO₂ nanoparticles synthesized via sol-gel were homogenously dispersed in the epoxy-rich phase. The morphology of the inorganic/organic epoxy based composites consisted of both well-dispersed TiO₂ nanoparticles and microphase separated PS block in the continuous PEO block/epoxy-rich phase since block copolymer acted as templating agent for selective location of TiO₂ nanoparticles. Differential scanning calorimetry (DSC) was used to study the curing behavior and the influence of the type and quantity of modifier on the glass transition temperature of epoxy matrix. Additionally, optical properties, transparency and UV-shielding efficiency of these new multiphase advanced thermosetting materials were also investigated.     

Microstructure and indentation damage resistance of ZrB2‐20 vol.%SiC ipo‐eutectic composites

Zirconium diboride with 20 vol.% silicon carbide bulk composites were fabricated using directionally solidification (DS) and also by spark plasma sintering (SPS) of crushed DS ingots. During the DS the cooling front aligned the c‐axis of ZrB₂ grains and its Lotgering factor of f_(00l) was high as 0.98. The Vickers hardness was anisotropic and it was high as 17.6 GPa along the c‐axis and 15.3 GPa when measured in an orthogonal direction. On both surfaces, even when using 100 N indentation load, no cracks were observed, suggesting a very high resistance to crack propagation. Such anomalous behavior was attributed to the hierarchical structure of DS sample where the ZrB₂ phase was under strong compression and the SiC phase was in tension. In the SPSed sample, the microstructure was isotropic respect to the direction of applied pressure. Indentation cracks appeared around the indent corners but not emanated from the diagonals, confirming high damage resistance.     

Dielectric strength of Al2O3/silicone composites after high‐temperature aging

Silicones are widely used for electrical insulation owing to their high dielectric strength and thermal stability. However, recent studies revealed insufficient stability of silicone for high‐temperature applications. To study the effect of Al₂O₃ fiber on silicone stability, we measured the dielectric strength of unfilled silicone and Al₂O₃/silicone composites as a function of aging time at 250°C in air and analyzed data by Weibull probability distribution to determine characteristic dielectric strength (E₀) and shape parameter (β). Prior to aging, unfilled silicone and composites had similar behavior, with E₀ at about 20 kV/mm and β > 15. During aging, unfilled silicone developed both micro‐ and macrocracks, with β dropped below five in 240 h and E₀ decreased significantly. Composites developed microcracks, with β dropped below 5 in longer time and E₀ remained almost constant. Addition of Al₂O₃ slowed down crack growth in silicone matrix, resulting in longer lasting high‐temperature dielectric materials. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41170.     

Improving thermo‐oxidative degradation resistance of bamboo fiber reinforced polymer composites with antioxidants. Part II: Effect on other select properties

The first of this two‐article study showed that the addition of antioxidants can significantly improve the thermo‐oxidative resistance of bamboo fiber reinforced polypropylene composites (BFPCs). In this article, the effect of antioxidants on water absorption, thermal stability, crystallinity, and the dynamic mechanical properties of the composites were investigated. The results showed that the addition of antioxidants resulted in a slight increase in water absorption, but this increase can be reduced by controlling the ratio of the primary and secondary antioxidants. The glass transition temperature (T_g) of composites also slightly increased. However, the effects of antioxidants on the crystallinity as well as other thermal properties of BFPCs were small or even insignificant. The different combinations, ratios, and the adding amounts of antioxidants show tiny differences for all these properties. As a whole, the addition of minor antioxidants in the bamboo fiber (BF) polymer composites will not produce obvious negative effects on their overall performances. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44199.     

PolyHIPE/pullulan composites derived from glycidyl methacrylate and 1,3‐butanediol dimethacrylate‐based high internal phase emulsions

Highly porous composites of poly(glycidyl methacrylate‐co‐1,3‐butanediol dimethacrylate) and pullulan were prepared as semi‐interpenetrating polymer networks by cross‐linking of high internal phase emulsions (HIPEs). HIPEs were prepared by using an aqueous phase made of pullulan dissolved in deionised water. Instead of conventional cross‐linkers such as divinyl benzene, 1,3‐butanediol dimethacrylate was used as a flexible co‐monomer. Morphological and mechanical properties of the porous composites with an initial pullulan loading ranging from 1 to 10 wt % have been investigated. Resulting composites were tested in terms of uniaxial compression stress and it was found out that the use of pullulan and flexible co‐monomer in the HIPE preparation increases the compression modulus from 13.53 to 30.8 MPa. Textural analyses of the resulting composites show that in all cases open cellular foams composed of primary cavities (～112–74 μm) connected with secondary interconnected pores were produced with a specific surface area in the range of 1.7–3.0 m² g^?1. In addition, the influence of using porogen in the oil phase was investigated. It was found that using a porogen reduces the cavity size diameter from ～112 to 20 µm and increases the compression modulus from 13.53 to 47.06 MPa. POLYM. ENG. SCI., 55:2636–2642, 2015. © 2015 Society of Plastics Engineers